Double angle cutoff die and method for rolling screws

ABSTRACT

This invention relates to gimlet point screws and thread rolling dies for making such screws. A full precisely formed gimlet point is achieved by means of an extruding cutoff ramp having a high rate of penetration initially followed by a more gradual penetration to remove the extrusion slug.

o United States Patent [191 3,78%33 Dickson Feb. 5, 11974 DOUBLE ANGLECUTOFF DIE AND 3,217,530 11/1965 Sato 72/469 METHOD FOR ROLLING SCREWS3,176,491 4/1965 Mau et al.. 72/88 3,726,171 "4/1973 Strybel 83/643 [75]Inventor: Joseph F. Dickson, Oxford, Mass.

73 A z RdRlldTh dDiC sslgnee ffi r j rea e ompany PrimaryExaminer-Milton S. Mehr [22] Filed: Feb. 10, 11972 [21] Appl. No.:225,242 [57] ABSTRACT [52] US. Cl. .1 72/469, 10/152 This inventionrelates to gimlet point screws and [51] Int. Cl 1321b 3/06 threadrolling dies for making such screws. A full pre- Field of Search ciselyformed gimlet point is achieved by means of an /643 extruding cutofframp having a high rate of penetration initially followed by a moregradual penetration [5 6] 1 References Cited to remove the extrusionslug.

UNITED STATES PATENTS 3,538,739 11/1970 Orlomoski 72/469 12 Claims, 8Drawing Figures PMENTED 74 SHEET 101 2,

BACKGROUND OF THE INVENTION The field of this invention pertains tomethods and tools for rolling threads on workpieces as they pass betweena pair of elongated generally planar dies which are relatively displacedto produce surface material flow on the workpiece to form a continuousthread. More particularly, the invention pertains to means for rollinggimlet point screws utilizing a single multiplane face of each of thetwo dies- These dies allow the use of straight, i.e., cylindrical blanksto be used as opposed to blanks having preformed points. The use of suchdies reduces the headed blank costs as well as the size of blankinventories.

The present invention has been found to be most useful with respect toflat rolling dies in conventional thread rolling machines. In suchmachines the shorter of a pair of dies is ordinarily held stationarywhile the longer die is moved in a direction parallel to a longitudinalreference plane in which the axis of rotation of the body portion of theworkpiece travels as the workpiece rolls between the pair of dies.Ordinarily no appreciable axial movement of the workpiece occurs duringthe rolling operation. The diameter of the finished thread is controlledby the diameter of the blank and the distance between the dies at thefinish end of the stroke. The workpiece typically will be steel althoughany extrudable commerciallyemployed material may be used.

Various dies have been devised in the past to produce gimlet pointscrews from cylindrical blanks such as that described in Mau et al US.Pat. No. Re26,5 l 8. Screws produced in accordance with the diesdescribed therein are sometimes vulnerable to bad point formation.Specifically, the points may be stringy or not solid because the finalpoint formation must necessarily occur over a relatively short distance.The rate of final point formation in such dies is the same as the rateused in rough forming the point initially from the cylindrical blank. Aclosely. related problem that occurs with such dies is that poor pointthread formation may occur because there are rlatively few ridgesavailable on the point threading surface to form the point threads.

Another problem which has occurred with such designs is that themovement of metal with some materials is sufficiently slow to create awork hardening effect that impedes subsequent formations. This problemis most acute in the formation of gimlet points since such points areformed after the body threads have begun to be formed. It is also mostacute with certain materials that are particularly vulnerable to workhardening such as 300 series stainless steel or C-l022 carbon steelwhich, because of its manganese composition, is more vulnerable to workhardening.

Accordingly, a primary object of this invention is to provide dies forrolling and a method for rolling gimlet point screws wherein full pointsand point thread formations are consistently produced.

Another object of the present invention is to provide dies which are ofminimum length and which minimize cold working effects on the screwblank.

Still another object is to provide amethod and an apparatus wherein theslug cutoff is delayed until a relatively full, sharp .point isproduced.

A further object of the invention is to gradually urge a slug of excessmaterial away from the screw point during the final forming andthreading thereof.

SUMMARY OF THE INVENTION It has now been found that the foregoing andrelated objects'can be readily attained in dies for forming thecircumference of a cylindrical workpiece and for severing thecylindrical workpiece. The dies have a first surface for forming thecylindrical workpiece having a mean or average plane which will becoincident with the first surface if the surface is planar. A cutofframp is disposed in upstanding relationship to the mean plane forsevering the, cylindrical workpiece having a first plane inclined at afirst angle to the mean plane and a second plane inclined at a secondangle to the mean plane. The angles will always be different althoughmost preferably the first angle is greater than the second angle. In itspreferred aspect, the dies have a generally planar second surfaceextending between the first surface and the cutoff ramp. The secondsurface is obliquely disposed with respect to the mean plane to form apointed surface on a workpiece adjacent to the end formed when thecutoff ramp severs the cylindrical workpiece.

In one preferred'form wherein the first plane engages the workpiecebefore the second plane, the cutoff ramp penetrates into the workpiecethree quarters of its total penetration in the first one-half of itslength which contacts the workpiece. In another preferred form thecutoff ramp penetrates seven-eights of its maximum penetration into theworkpiece after three quarters of the length of the cutoff ramp haspassed over the cylindrical workpiece.

The invention also contemplates the method of severing the end of acylindrical workpiece comprising urging a first portion of an upstandingcutoff ramp having a generally planar outer face against onelongitudinal portion of the cylindrical workpiece as it is rotated, andthen urging a second portion of the cutoff ramp inclined at a differentangle than the first portion against the one longitudinal portion ofsaid cylindrical workpiece so that the rate of penetration into thecylindrical workpiece vaires between the first and second portions.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top plan view to a greatlyenlarged scale of the short die of a pair of thread rolling dies inaccordance with the invention;

FIG. 2 is a side elevational view to a greatly enlarged scale of a pairof thread rolling dies consisting of the short die in FIG. 1 togetherwith a long die in the matched position with a screwblank therebetween;

FIG. 3 is a top plan view to a greatly enlarged scale of the die shownin FIG. 1 before ridges and traction notches have been formed thereinshowing the planar faces on the top surface of the die more clearly;

FIG. 4 is a transverse sectional view to a greatly enlarged scale takenalong the line 4-4 of FIG. 2 when these lines on the upper and lowerdies are in vertical alignment prior to horizontal movement of the longdie to the left as viewed to the FIG. 2 position and with a diameter ofthe workpiece alignedgwith the section lines but with the threadsomitted to more clearly show the extruding action of the dies in formingthe gimlet point; I

FIG. 5 is a transverse sectional view to a greatly enlarged scale takenalong the line 5-5 of FIG. 2 when these section lines on the upper andlower dies are in vertical alignment prior to horizontal movement of thelong die to the left as viewed to the FIG. 2 position and with adiameter of the workpiece aligned with these lines but with the threadsomitted to more clearly show the extruding action of the dies in formingthe gimlet point;

FIG. 6 is a transverse sectional view to a greatly enlarged scale takenalong the line 66 of FIG. 2 when these section lines on the upper andlower dies are in vertical alignment prior to horizontal movement of thelong die to the FIG. 2 position and with a diameter of the workpiecealigned with the section lines but with the threads omitted to moreclearly show the formation of the gimlet point;

FIG. 7 is a transverse sectional view to a greatly enlarged scale takenalong the line 77 of FIG. 2 when these section lines on the upper andlower dies are in vertical alignment after horizontal movement of theupper die from the FIG. 2 position and with a diameter of the workpiecealigned with these section lines but with the threads omitted to moreclearly show the point formation; and

FIG. 8 is a transverse sectional view to a greatly enlarged scale takenalong the line 88 of FIG. 2 when these section lines on the upper andlower dies are in vertical alignment after horizontal movement of theupper die from the FIG. 2 position and with a diameter of the workpiecealigned with these section lines but with the threads omitted to moreclearly show the point formation.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT Turning now in detailto FIGS. 1, 2 and 30f the drawings, therein illustrated is a short die10 embodying the present invention and having a plurality of discreteregions, each of which is adapted to operate in conjunction with acorresponding region on a long die 12 to vary the form of a blank orworkpiece 14 having a cylindrical body portion 16 and a head 18. As iscustomary in such dies, there is an exact counterpart having identicalshape and size on the long die for every portion of the short die exceptthe end portions. The long die 12 is provided with extensions whichtypically may be one quarter of one inch on each end. The extensions areprovided for end-wise adjustment purposes.

Referring now particularly to FIG. 3, the discrete transverse regions ofshort die 10 are identified by letters A through F. During the rollingoperation, the workpiece 14 is rolled from region B on short die 10 andlong die 12 to region E on short die 10 and long die 12. Regions A and Fare the sloping end portions by which the die is mounted. Region B isthe point relief area in which the screw blank is first positionedbetween the dies. Region C includes the cutoff or extruding ramp firstplane 20 in which the ramp penetrates the workpiece cylindrical portion16 at a high rate. In region D the angle of incidence of the cutoff rampwith respect to the workpiece is altered and a cutoff ramp second plane22 thereof continues to penetrate the workpiece at a lower rate. The endof the cutoff ramp occurs at the end of region D at which time theextrusion slug 23 is fully formed although not yet severed from thecylindrical body portion 16 of the workpiece.

FIG. 7 best illustrates this action. In region E the point threadingsurface 24, which started in region C, continues to fully form thethreads on the gimlet point which has been fully formed at the end ofregion D. A planar land surface 26 is parallel to the base 27 of theshort die 10 as well as to plane Z which is defined by the successivepositions of the longitudinal axis of the cylindrical portion 16 ofblank 14. This surface 26 provides the final severance of the extrusionslug 23 as the corresponding surface 26 from the long die bears againstit and increases in width as the workpiece cylindrical portion 16 passestherebetween. The body threading surface 28 extends through regions B, CD and E and provides for threading of the body in a conventional manner.Back taper portion 30 is provided to urge the extrusion slug 23 awayfrom the pair of dies 10 and 12. Back cut surface 32 is cut away toprovide an area for the extrusion slug 23 to drop away. Region E is thefinish dwell and rolloff area which is provided to guide the fullyformed screw away from the dies 10 and 12.

Turning now to the specific contours of the various surfaces within thedefined regions, the first plane 20 of the extruder or cutoff ramp issubstantially trapezoidal having converging sides 34 and 36 as well as aside 38 which is substantially parallel to the fourth side which is notillustrated in the drawings although it is coextensive with a lineperpendicular to the longitudinal center line of the short die 10 andseparating regions B and C. Surface 40 is coplanar with cutoff rampfirst plane 20 but is considered a discrete surface because the cutoffor extrusion has not yet begun which forms the gimlet point as isapparent by reference to FIG. 4. It will be observed there that thecylindrical surface 16 of the workpiece 14 has not yet been deformedalthough it is gripped by the body threading portion 28. The bodythreading portion 28 is provided with a plurality of ridges 42 whichform the body threads on the workpiece 14 as well as a plurality ofcrossnicks or traction notches as described in Orlomoski US. Pat. No.3,405,545 having the same assignee as the present invention. Thetraction notches avoid slippage of the workpiece with respect to the dieduring the rolling operation. The body threading portion 28 lies betweenthe edge 46 of the top surface of the die and heel line 48 which definesthe intersection between the body threading surface 28 and the pointthreading surface 24. Surface 24 is bounded on the opposite side by edge34 of cutoff ramp first plane 20, edge 50 of cutoff ramp second plane 22and edge 52 of surface 26. Ridges 54 are provided on the point threadingsurface 24 in the conventional manner. The body threading surface 28 isdisposed substantially parallel to the base 27 of short die 10. Pointthreading surface 24 is disposed at an angle corresponding to the angleof the gimlet point of the screw as is best seen by reference to FIGS. 5through 8. The angle will not change throughout the length of the pointthreading surface 24 although as is most evident in FIG. 3 the width ofthis surface will vary.

Extrusion ramp first plane 20 forms an angle with reference plane Z andalso base 27 which is most evident in FIG. 2 wherein edges 34 and 36 areclearly shown. It will be seen that an angle is formed between referenceplane Z and extruder ramp first plane 20 when short die 10 is viewedlengthwise as in FIG. 2. The size of this angle will be discussedhereafter. It is also evident from FIG. 2 that viewing the end of die 10that the extrusion ramp first plane 20 is canted at an angle. Th'atangle which tends to force the extrusion slug 23 away fromthecylindrical surface 16 of the workpiece 14 will normally be less thantwenty degrees.

Similarly, the cutoff ramp second plane 22 will have an angle withrespect to reference plane Z which when viewed from the end'of short diewill also normally be less than 20. The angle of this same surface whenviewed from the side as in FIG. 2 is indicated by the edges shown inthat view. Both the cutoff ramp first plane 20 and second plane 22 areprovidedwithtraction notches 58 which are desirable to insure that theextrusion slug 23 is forced to rotate with the cylindrical portion 16 ofthe workpiece 14. The land surface 26 has diverging edges 52 and 60which urge the extrusion slug 23 away from the cylindrical portion 16after the extrusion slug 23 has been fully formed..The land surface 26is-normally substantially parallel to reference plane Z and the sidesthereof diverge at an angle of approximately fifteen degrees. Widevariations in this angle are necessary with various screw sizes. Theback taper portion 30 of the die is adjacent to the land surface 26 andis also bounded by an arcuate portion 62 of the back cut surface 32.Oblique end surfaces 66, 68 are provided on short die 10 for gripping bythe thread rolling machine. Similarly, oblique ends 70, 72 are providedon long die 12 for gripping by the thread rolling machine.

It should be understood that the cutoff ramp extends the length ofregions C and D. Stated another way, the cutoff ramp extends the lengthof extrusion ramp first plane 20 and extrusion ramp second plane 22. Thetotal length ordinarily corresponds to about three complete turns of theworkpiece 14. It should be understood however that the length may varyand that a length corresponding to as manyas five turns may be providedwith the length being largely dependent upon the size of the screw beingrolled and the positioning of the holders for the dies in the threadrolling machine being used. The length of the cutoff ramp may also bedefined asthe length of the top surface (regions B, C, D and E) less thelength-of the point .relief area (region B) and the length of the dwelland rolloff area (region E). Region E is normally equal in length to oneto one and one-half blank circumferences plus the length of rolloff. Thelength of rolloff will normally be about one screw major diameter.Region B is the length of point relief which normally will be fixed forany one size of die. The length corresponding to specific dies which arenormally used are No. 00 3/16 inch, No. 0 3 1 inch, No. 10 inch, and No.20 4 inch. It will be understood by those skilled in the art thatnormally any one rolling machine will hold only one length of die andalso that any one die may be used for a number of sizes. Accordingly,the number of blank circumferences equal to the cutoff ramp length willvary when different sizes of blanks are rolled on the same die.

The distance between the projection of the heel line 48 and point 74,which is sometimes referred to as point X on a horizontal plane as inFIG. 3, corresponds to the point constant of the gimlet point screwbeing rolled. The point constant of thegimlet point screw is thelongitudinal distance between the extreme tip of the point and the endof sloping surfaces leading away from the point. This dimension has beenlabeled PC in FIG. 8. The distance between the projection of point 74and heel line 48 on a' vertical plane 'as in FIG. 2 is known as theheight of curve. Since the angle between body threading surface andpoint threading surface 24 for any one die is constant, the ratio of l)the vertical distance of any point on edge 50 or 34 to the heel line 48to (2) the horizontal distance of that point on edge 50 or 34 to theheel line 48 is equal the ratio of the height of curve and pointconstant. For any specific gimlet point screw, the dimensions of thepoint constant and the height of curve dimensions of the die are fixed.Other variations in the cutoff ramp are a matter of the designerschoice.

It has been found empirically that optimum point formation occurs whenthe intersection of edge 34 and edge 22 respectively of cutoff rampfirst plane 20 and cutoff ramp second plane 22 is positioned so as tobe, when projected in a top plan view such as FIG. 3, a horizontaldistance from the heel line 48 equal to threefourths of the pointconstant distance mid-way between the ends of the cutoff ramp. Asexplained above, the ratio of the vertical height to the verticaldistance of a point on the inner edge of the cutoff ramp is equal to theratio of the height of curve to the point constant. Accordingly, theedge 34 of cutoff ramp first plane 20 is diverging rapidlyfrom heel line48 in region C as projected in a horizontal plane such as FIG. 2. It isalso diverging from heel line 48 as projected in a vertical plane, as inFIG. 3, an amount proportionate to the ratio of the point constant tothe height of curve. It follows that a point on first plane edge 34which has a horizontal height from heel line 48 equal to three-fourthsof the point constant distance has also a horizontal dis.- tance fromthe heel line equal tothree-fourths of the height of curve. In otherwords in the first form the cutoff ramp innersurface penetratesthree-fourths of the point constant distance in one-half of the lengthof the cutoff ramp.

In another preferred form edges 34 and 50 intersect at apoint which isthree-fourths of the length of the cutoff ramp with seven-eighths of thepoint constant. In the second form, the cutoff ramp innersurfacepenetrates seven-eighths of the point constant in threefourths of thelength of the cutoff ramp.

The size that is most desirable will vary with the size of the screwbeing rolled. More particularly, this latter embodiment has been foundparticularly satisfactory with No. 12 screw diameters as well as largersizes. The first embodiment has been most successful with No. 0 throughNo. 10 screw diameters.

As noted before, the long die 12 is provided with an exact counterparthaving identical shape in size of each portion of the short die with theexception that extensions which typically may be in the order of onequarter of an inch are provided which increase the length of thepointrelief area (region B) and the finish relief area (region E). Thelengths of regions C and D in short die 10 and long die 12 are identicaland the distances between the section shown in FIGS. 4, 5, 6, 7 and 8are identical in the'two dies.

Turning now in detail to FIGS. 4, 5, 6, 7 and 8 the functioning of theshort die 10 in cooperation with the long die 12will be more apparent.The workpiece 14 is fed between body threading surfaces 28 of short die10 and long die 12. FIG. 4 as well as FIGS. 5,6, 7 and 8 have beensimplified by eliminating the threads to show in greater detail thepoint forming action of the dies. As'long die 12 is longitudinallydisplaced, the workpiece is passed from region B to region C andspecifically to the position shown in FIG. wherein point threadingsurface 24 has started and as will be apparent in succeeding sectionalviews and also from FIG. 3 that surface is increasing its contact withthe cylindrical surface 16 of the workpiece 14. Also, at thiscrosssectional point, the cutoff ramp 20 has begun to contact a portionof the cylindrical body portion 16 of the workpiece 14 and has begun toform the extrusion slug 23 and to urge it away from the head 18 of theworkpiece 14. In FIG. 6 is shown the operation of the various surfacesof the dies 10 and 12 at a point shortly after the workpiece 14 has beenrolled into region D. It will be seen that the bulk of the extrusionslug 23 has been formed and that most of the point of the workpiece hasalso been formed by point threading surfaces 24. The penetration of thecutoff ramp first plane has been completed at this cross-sectionalpoint, and it is most apparent that the bulk of its penetration into theworkpiece 14 cylindrical portion 16 has occurred at this cross-sectionalposition.

Referring now to FIG. 7, the section shown is the beginning of region E,After the workpiece 14 has moved further past point 74, the extrusionslug 23 has been fully formed and further movement of the workpiece 14toward the end of the dies 10 and 12 will cause the back taper portionto sever the extrusion slug 23 from the rest of the workpiece 14. In thetransverse cross-section shown in FIG. 8, the extrusion slug 23 has beencompletely severed and the workpiece has been completely formedpreparatory to being ejected from the dies.

Although the present invention has been illustrated and described withrespect to a particular form of flat die, it should be appreciated bythose skilled in the art that it also has application for use withplanetary dies and with respect to forming various surfaces includingdouble lead screws as well as single lead screws and also in rollingother desired forms applied by rolling instead of merely threads. Thelocation of the intersection of cutoff ramp first plane 20 and secondplane 22 will vary with the size of the screw blank. The angle of theextruder ramp with respect to reference plane Z as viewed from the endof the die may vary between 0 and 20 although an angle of 15 is mostcommonly used. Also, this angle may vary throughout the length of theextruder ramp and may for example be initially 15 and then may beincreased to 20 at a point of later contact with the workpieceparticularly in the area near where the extrusion slug 23 is severed.Many of the other surfaces may be varied to a substantial degree withoutdeparting from the invention.

Thus, it can be seen from the foregoing detailed specification anddrawings that the present invention provides a highly effective cutoffdie and method for rolling screws which is capable of forming fullpoints and point thread formations in a consistent manner. The dies bycombining a cutoff ramp having a rapid rate of penetration or initialformation initially followed by a slow or final rate of penetration orfinal formation provide the full point without the necessity for anextremely long die which would otherwise be necessary to accomplish thedesired result and which would produce undesirable cold working effects.The slower rate of final penetration or formation gradually urges theextrusion slug away from the screw point during the final forming andthreading thereof.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A roll forming die for forming the circumference of a cylindricalworkpiece and for pointing and severing the cylindrical workpiecewherein the die is provided with (a) a first surface for forming a bodyportion of a cylindrical workpiece, said first surface having a meanplane and (b) a cutoff ramp upstanding from said mean plane for pointingand severing the cylindrical workpiece, said cutoff ramp rising fromsaid first surface of the die for forming the workpiece and having afirst plane inclined at a first angle to said mean plane and a secondplane inclined at a second angle to said mean plane, said second anglebeing different than said first angle, said cutoff ramp having a pointthreading surface on the side thereof between said mean plane and theuppermost portion of said cutoff ramp.

2. A die as set forth in claim 1 wherein said first angle is greaterthan said second angle.

3. A roll forming die as set forth in claim 2 wherein a generally planarsecond surface extends between said first surface and said cutoff ramp,said second surface being obliquely disposed with respect to said meanplane to form a pointed surface on the workpiece adjacent to the endformed when said cutoff ramp severs the cylindrical workpiece.

4. A roll forming die as set forth in claim 3 wherein said first andsaid second surfaces are provided with a plurality of ridges for forminga continuous thread on the cylindrical workpiece.

5. A roll forming die as set forth in claim 4 wherein said first planeengages said workpiece before the second plane and said cutoff ramppenetrates into the workpiece three quarters of its total penetration inthe first one-half of its length which contacts the workpiece.

6. A roll forming die as set forth in claim 4 wherein said first planeengages said workpiece before said second plane and said cutoff ramppenetrates seven-eights of its maximum penetration into the workpieceafter three quarters of the length of the cutoff ramp has passed overthe cylindrical workpiece.

7. A pair of roll forming dies for forming the circumference of acylindrical workpiece and for pointing and severing the cylindricalworkpiece wherein each die is provided with (a) a first surface forforming a body portion of a cylindrical workpiece, said first surfacehaving a mean plane and (b) a cutoff ramp upstanding from said meanplane for pointing and severing the cylindrical workpiece, said cutofframp rising from said first surface of the die for forming the workpieceand having a first plane inclined at a first angle to said mean planeand a second plane inclined at a second angle to said mean plane, saidsecond angle being different than said first angle, said cutoff ramphaving a point threading surface on the side thereof between said meanplane and the uppermost portion of said cutoff ramp.

8. A pair of dies as set forth in claim 7 wherein said first angle isgreater than said second angle.

9. A pair of roll forming dies as set forth in claim 8 wherein each ofsaid dies has a generally planar second surface extending between saidfirst surface and said cutoff ramp, each of said second surfaces beingobliquely disposed with respect to said mean plane to fonn a pointedsurface on said workpiece adjacent to the end formed when said cutofframp severs the cylindrical-workpiece.

10 piece.

12. A pair of roll forming dies as set forth .in claim 10 wherein saidfirst plane of each die engages said workpiece before said second planeand said cutoff ramp penetrates seven-eighths of its maximum penetrationinto the workpiece after three quarters of the length of the cutoff ramphas passed over the workpiece.

v UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,789,643 Dated Febru gry 5, 1974 Inventor-(s) Joseph F. Dickson It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

In The Assigneesv O Delete "Reed Rolled Thread Die Company" andsubstitute therefor --Litton Industrial Products, Inc.--.

In The Specification:

Column 1, line: 4f), delete "rlatively" and substitute therefor--relatively--.

Column 2, line 44, delete "vaires" and substitute therefor --varies-.

Signed and sealed this 16th day of July 1974.

(SEAL) Attest:

McCOY GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents FORM PC4050 (10-69)

1. A roll forming die for forming the circumference of a cylindricalworkpiece and for pointing and severing the cylindrical workpiecewherein the die is provided with (a) a first surface for forming a bodyportion of a cylindrical workpiece, said first surface having a meanplane and (b) a cutoff ramp upstanding from said mean plane for pointingand severing the cylindrical workpiece, said cutoff ramp rising fromsaid first surface of the die for forming the workpiece and having afirst plane inclined at a first angle to said mean plane and a secondplane inclined at a second angle to said mean plane, said second anglebeing different than said first angle, said cutoff ramp having a pointthreading surface on the side thereof between said mean plane and theuppermost portion of said cutoff ramp.
 2. A die as set forth in claim 1wherein said first angle is greater than said second angle.
 3. A rollforming die as set forth in claim 2 wherein a generally planar secondsurface extends between said first surface and said cutoff ramp, saidsecond surface being obliquely disposed with respect to said mean planeto form a pointed surface on the workpiece adjacent to the end formedwhen said cutoff ramp severs the cylindrical workpiece.
 4. A rollforming die as set forth in claim 3 wherein said first and said secondsurfaces are provided with a plurality of ridges for forming acontinuous thread on the cylindrical workpiece.
 5. A roll forming die asset forth in claim 4 wherein said first plane engages said workpiecebefore the second plane and said cutoff ramp penetrates into theworkpiece three quarters of its total penetration in the first one-halfof its length which contacts the workpiece.
 6. A roll forming die as setforth in claim 4 wherein said first plane engages said workpiece beforesaid second plane and said cutoff ramp penetrates seven-eights of itsmaximum penetration into the workpiece after three quarters of thelength of the cutoff ramp has passed over the cylindrical workpiece. 7.A pair of roll forming dies for forming the circumference of acylindrical workpiece and for pointing and severing the cylindricalworkpiece wherein each die is provided with (a) a first surface forforming a body portion of a cylindrical workpiece, said first surfacehaving a mean plane and (b) a cutoff ramp upstanding from said meanplane for pointing and severing the cylindrical workpiece, said cutofframp rising from said first surface of the die for forming the workpieceand having a first plane inclined at a first angle to said mean planeand a second plane inclined at a second angle to said mean plane, saidsecond angle being different than said first angle, said cutoff ramphaving a point threading surface on the side thereof between said meanplane and the uppermost portion of said cutoff ramp.
 8. A pair of diesas set forth in claim 7 wherein said first angle is greater than saidsecond angle.
 9. A pair of roll forming dies as set forth in claim 8wherein each of said dies has a generally planar second surfaceextending between said first surface and said cutoff ramp, each of saidsecond surfaces being obliquely disposed with respect to said mean planeto form a pointed surface on said workpiece adjacent to the end formedwhen said cutoff ramp severs the cylindrical workpiece.
 10. A pair ofroll forming dies as set forth in claim 9 wherein said first and saidsecond surfaces are each provided with a plurality of ridges for forminga continuous thread on the cylindrical workpiece.
 11. A pair of rollforming dies as set forth in claim 10 wherein said first plane engagessaid workpiece before said second plane and said cutoff ramp penetratesinto the workpiece three quarters of its total penetration in the firstone-half of its length which contacts the workpiece.
 12. A pair of rollforming dies as set forth in claim 10 wherein said first plane of eachdie engages said workpiece before said second plane and said cutoff ramppenetrates seven-eighths of its maximum penetration into the workpieceafter three quarters of the length of the cutoff ramp has passed overthe workpiece.